1. Field of the Invention
The invention relates to a rotary electric machine, and a method for controlling the rotary electric machine.
2. Description of the Related Art
In rotary electric machines such as electric motors, power generators, and motor generators, the temperature of coils of a stator increases during operation.
Therefore, a method of measuring the temperature of a coil by pressing a temperature sensor against the coil is employed (refer to, for example, Japanese Patent Application Publication No. 2003-92858 (JP 2003-92858 A)). In recent years, alternating-current (AC) motors and alternating-current (AC) motor generators, in which a magnet is embedded in a rotor, have been in widespread use. In this type of rotary electric machine in which a magnet is embedded in a rotor, the temperature of the magnet of the rotor increases during operation. Therefore, a cooling oil passage that extends along the magnet is formed in the rotor, and the magnet is cooled by passage of cooling oil through the cooling oil passage. However, it is difficult to directly measure the temperature of the magnet because the magnet rotates together with the rotor. Therefore, there is proposed the following method. According to the method, cooling oil for a magnet is supplied from an outlet of a cooling oil passage, in the radial direction, toward a temperature sensor fitted to a stator, and the temperature of the cooling oil, which has cooled the magnet and therefore the temperature thereof has increased, is detected by the temperature sensor. In this way, the temperature of the magnet is estimated. According to this method, the flow rate of coolant for the magnet is increased or decreased based on the estimated temperature of the magnet (refer to, for example, Japanese Patent Application Publication No. 2008-178243 (JP 2008-178243 A)).
Also, the following method of cooling a coil end of a stator is employed. According to this method, a cooling oil passage is formed in a rotor, and cooling oil is supplied from the rotor toward the coil end in the radial direction to cool the coil end (refer to, for example, Japanese Patent Application Publication No. 2009-284718 (JP 2009-284718 A)). In this method, providing a guide member that guides the cooling oil to the coil end is proposed so that the cooling oil is effectively supplied to the coil end. JP 2009-284718 A also proposes a method of providing heat protection to the coil end. According to this method, a temperature sensor is fitted to the coil end at a portion that is less likely to contact the cooling oil to detect the highest temperature in the coil end.
In recent rotary electric machines, a method of supplying cooling oil toward a coil end of a stator from a position over the coil end in the vertical direction is often employed to cool the stator further efficiently. In this case, in order to provide heat protection to both of the coil and the cooling oil, a load of the rotary electric machine is restricted to keep the temperature of the coil below a predetermined upper limit temperature and keep the temperature of the cooling oil below a predetermined upper limit temperature. When the flow rate of the cooling oil is changed, it is necessary to control the flow rate of the cooling oil such that the temperature of the coil falls within a predetermined temperature range and the temperature of the cooling oil falls within a predetermined temperature range. For example, the flow rate of the cooling oil is controlled such that the flow rate of the cooling oil is low when the temperature of the coil is low, and the flow rate of the cooling oil is increased with an increase in the temperature of the coil. In addition, when the temperature of the cooling oil itself increases with an increase in the temperature of the coil, the flow rate of the cooling oil is reduced such that the temperature of the cooling oil itself falls below an upper temperature limit. In other words, when the temperature of the cooling oil is low, the flow rate of the cooling oil is determined in accordance with the temperature of the coil, and when the temperature of the cooling oil increases to a certain degree, the flow rate of the cooling oil is determined in accordance with the temperature of the cooling oil itself.
In this case, it is necessary to detect both the temperature of the coil and the temperature of the cooling oil. However, in each of the related arts described in JP 2003-92858 A, JP 2008-178243 A, and JP 2009-284718 A, measuring only one of the temperature of the coil and the temperature of the cooling oil is suggested. Therefore, in order to detect both the temperature of the coil and the temperature of the cooling oil itself, provision of a plurality of temperature sensors is required. This may complicate the configuration.